(1) Field of the Invention
The present invention relates to a procedure for the detection and display of the ground and of artificial obstacles present in the field of detection, of detection means installed on board a vehicle, and particularly on board a rotary-wing aircraft.
(2) Description of Related Art
Such a procedure is preferably, but non-limitatively, implemented in conjunction with detection means, such as a LIDAR detector, whose acronym corresponds to the English phrase “Light Detection and Ranging”, or a RADAR detector, whose acronym corresponds to the English phrase “Radio Detection and Ranging”. Such detection means may also consist of a stereoscopic or three-dimensional imaging system.
In order to allow the detection and display of the ground, the terrain, and artificial obstacles such as a tower, a pylon, or an electrical power line, such a procedure must be sufficiently reliable and rapid. In particular, it must process the detected data as rapidly as possible, in order to be able to deliver in real-time, to a human or automatic driver or pilot of the vehicle, the information that will make it possible to identify and avoid such obstacles.
More specifically, such reliable and rapid information for the detection of the ground and of obstacles is necessary, or even essential, for the pilot of an aircraft flying close to the ground under impaired visibility conditions, in order to allow the obstacles to be overflown and avoided.
It is known that detection means that provide elementary echoes or plots based on the environment can be used to produce a database of the elevation of the terrain of the area observed by the detection means. This database includes the terrain and the obstacles. However, in its raw state this database also includes errors due to false echoes, which must be taken into consideration in order to be eliminated or corrected.
In particular, it is known that document FR 2888944 describes a procedure for the detection of the presence of at least one wireframe object suspended in the field of detection of a telemetry device, with the calculation of the ground coordinates of plots corresponding to the echoes delivered by the telemetry device. Candidate plots are selected from among these plots, and line segments in proximity to vertical projections of the candidate plots are determined. Last, a Hough transform is used to detect, in each vertical plane containing one of these line segments, portions of small chains near which the candidate plots are located. However, the use of such a Hough transform does not lead to optimal processing time.
Document FR 2953300 also describes a procedure for the detection of the presence of at least one suspended wireframe object, using the least-squares method, which makes it possible to reduce the calculation time.
Document FR 2953316 is also known, which describes a procedure for the detection of the terrain and of obstacles, which procedure makes it possible to eliminate detection errors caused by false echoes. In particular, a false echo is identified when an isolated plot is detected.
Furthermore, document U.S. Pat. No. 7,046,841 describes a method and a system for the analysis and detection of the environment by means of three-dimensional laser detection. This three-dimensional information is broken down into finite elements, with an eigenvalue and an eigenvector being associated with each finite element depending on the characteristics of the detected element, such as terrain, vegetation, a building, or an electrical power line. Thus, each external element can be identified.
Last, document US 2013/0257852 describes a synthetic vision system for the environment of a vehicle distinguishing, in particular, objects that are attached to the ground and objects that are detached from the ground. This system includes a database for the ground and for the obstacles attached to and detached from the ground; detection means, such as LIDAR detection means; calculation means; and display means. Thus, detected terrain surfaces are displayed based on information in the database, with the incorporation of the objects attached to the ground, as well as the obstacles corresponding to objects that are detached from the ground.
Furthermore, the technological background of the technical field of the invention includes several documents, including document US 2011/0282581, document US 2013/022197, and document U.S. Pat. No. 8,565,958. This technological background also includes the following publications: “Multi-resolution terrain depiction on an embedded 2D/3D synthetic vision system”, by Thomas Wiesemann, in Aerospace Science and Technology (Elsevier, September 2005); “Multi-level surface maps for outdoor terrain mapping and loop closing”, by Rudolph Triebel, presented at the IEEE International Conference on Intelligent Robots and Systems (October 2006); and “Processing of laser scanner data—algorithms and applications”, by Peter Axelsson, in Photogrammetry and Remote Sensing (Elsevier, July 1999).
Nevertheless, such systems based on detection means, image processing, and shape recognition employ substantial calculation resources and require significant amounts of calculation time. In particular, the recognition of the detected shapes and the detailed display of those shapes are major consumers of calculation resources and major generators of calculation time.